For the pastry, pulse all of the pastry ingredients in a food processor until the mixture just comes together as a dough. Tip the mixture out on a floured work surface and knead briefly until smooth. Roll the pastry out to as 3mm/⅛in thickness and use it to line a 20cm/8inch shallow tart tin. Chill in the fridge for two hours.
Preheat the oven to 200C/400F/Gas 6.
Line the pastry case with greaseproof paper and fill with baking beans. Bake the pastry for 15-20 minutes, then remove the greaseproof paper and baking beans, brush all over with the egg wash and cook for a further five minutes.
Meanwhile for the filling, cook the apples and sugar in a saucepan for 6-8 minutes, or until softened. Set aside to cool.
Drain the apple mixture and place it into a bowl with the passion fruit. Spoon the filling into the cooked pastry case.
For the meringue, whish the egg whites in a large bowl with an electric whisk until stiff peaks form. Slowly whisk in the sugar.
Spoon the meringue on top of the pie and tease into spikes with a fork.
Reduce the oven temperature to 180C/350F/Gas 4. Cook the pie for a further six minutes. (Alternatively you can brown the top of the meringue with a blow torch or by placing under a hot grill.)
Serve the pie with clotted cream.